There have been many investigations in the past for developing a convenient method for the selective preparation of mono-esters of polyols. Both enzymatically catalysed as well as non-enzymatically catalysed methods have been investigated. A review of the various ways in which this subject was investigated using enzymatically catalysed processes is given by U. T. Bornscheuer in "Enzyme and Microbial Technology", 17, 578-586, 1995.
An example of such a process, using enzymes having esterase activity, such as lipases or esterases, is given in European Patent Specification EP-B-0,215,038 (Novo Industri A/S). In this patent a process for the preparation of monoglycerides has been described in which first two hydroxyl groups of glycerol are blocked by converting them into a ketal or an acetal, such as isopropylidene glycerol or glycerol diethylketal. This ketal or acetal is then reacted with a carboxylic acid or a carboxylic acid ester in the presence of an esterase. The acetal or ketal protecting group is then removed by acid catalysis from the resulting ester to produce monoglyceride. This synthesis constitutes a rather cumbersome route, however, in that first two adjacent hydroxyl groups of the glycerol molecule need to be blocked involving chemical reaction and the blocking group has then to be removed in a final deprotection step.
Therefore, there is still a need for a simple enzymatic process for preparing fatty acid mono-esters of polyhydric alcohols which is economically attractive with regard to the price of the enzyme and which leads to high yields of monoglyceride and the smallest possible amount of di-esters or higher esters.
A group of closely related glycoproteins, known as patatin, is responsible for lipid acyl hydrolase activity found in potato tubers. The lipid acyl hydrolase is only known for its activity to catalyze the deacylation (hydrolysis) of a range of naturally occurring lipids, e.g. monoglycerides, diglycerides and phospholipids (Biochem. J. 121 (3), 379-390 (1971)).
The use of a lipid acyl hydrolase for the formation of wax esters from long chain monocarboxylic acids and long chain monohydric alcohols has been demonstrated (S. Dennis and T. Galliard, Phytochemistry 13 [11], 2469-2473 [1974]). It is surprising that the synthesis of polyol mono-esters, such as monoglycerides, has never been suggested or proposed.